The invention relates generally to sensor interrogation and more particularly to optical sensor interrogation.
Optical sensor systems in general have benefits over electrical systems due to electromagnetic interference (EMI) immunity, higher temperature operation, and ability to multiplex many sensor signals on the same transmission fiber. In optical sensor systems, the sensed parameter can be encoded as an intensity change, a wavelength shift, or a polarization change of the optical signal. Optical sensor systems based on wavelength encoding have the advantage of immunity to loss variation in the transmission medium.
Interrogation of optical wavelength sensors is typically implemented by measuring the optical power as a function of optical wavelength, as in an optical spectrum analyzer. One method for measuring this is to sweep a tunable optical filter over the spectrum of interest and record the power at different wavelengths using a photodetector. Another method is to spread the optical signal spatially using a prism or other wavelength dependent device and illuminate an array of photodetectors. In this method, each photodetector measures the power at a specific optical wavelength.
A challenge with interrogating optical sensors based on wavelength encoding is decoding of the wavelength at the processing end of the system with high speed and accuracy. Current optical interrogation systems typically achieve 10 to 1000 Hz data decoding rates. In many applications such as in control systems and in structural health monitoring, much higher rates, as high as tens of Megahertz, are required.
It would therefore be desirable to achieve higher data decoding rates without increased cost or complexity in the interrogation systems.